Swap a 1997 90 hp power head onto a 1989 85 hp?

[Tractor Jockey]

Hi Experts, has any one tried to swap a much newer power head on to a 1989 85 hp? The later power head has no acessorys, electronics etc. Problems and pit falls? All my acessorys are good, carbs etc. Thanks for any replies. Tractor jockey

 

[pnwboat]

Re: Swap a 1997 90 hp power head onto a 1989 85 hp?

One problem is that the crank shaft snout is a different diameter and ignition systems are different. What this means is that the flywheel on the 1997 motor and the 1989 motor are not interchangeable. If you can't mount your 1989 flywheel on the 1997 crank shaft, then you can't use the 1989 85HP Prestolite ignition system on the 1997 motor. You need the complete 1996 or later Mercury style CDM ignition stem for the 90hp MOTOR.

I've seen some complete used 1996 or later Force / Mercury CDM type ignition systems on some of the auctions sites from time to time.

 

[Frank Acampora]

Re: Swap a 1997 90 hp power head onto a 1989 85 hp?

However, the early crankshaft will swap into the 1997---only problem is that the rods, bearings, and pistons are different. So, you would need to find early pistons and re-use your rods.

All in all, too much bother to try it. better to find an earlier block.

 

[jerryjerry05]

Re: Swap a 1997 90 hp power head onto a 1989 85 hp?

Like the others said .NO
What's wrong with the block you have?

 

[Tractor Jockey]

Re: Swap a 1997 90 hp power head onto a 1989 85 hp?

Hi Frank, You make me laugh. You are so willing to give advise and I learn a lot from you guys. I would have just said NO it will not fit but you take the time to explain why...........Thanks a lot............Paul

 

[Tractor Jockey]

Re: Swap a 1997 90 hp power head onto a 1989 85 hp?

Jerry, Piston rings broke and gouged the cylinder walls (2) terrible. Mic'd the cylinders and cannot over bore to clean them up. The ring pieces worked up and out of the piston heads. I knew that I had a problem but was sure that it was a fuel issue. Sometimes the motor would run better, then other times would only run at 2,000 rpm. It was amazing that it got us back to the dock. Lake Pend Oreille is a good sized lake. I was sure that took good care of it, however now it is hurt bad.. I will keep looking for a motor. Thanks for the advise...........Paul